You have to learn ways to better APPROACH the exam itself to see improvement sometimes.
There is a lot more that goes into the GMAT than simply being able to solve questions. There is time-management, the way to "see" a cleaner path to solving a question, a way of thinking about questions as well that you can hope to leverage. This has nothing to with knowing formulas per se (yes, the a^2 - b^2 formula is pretty handy, though).
When it comes to Verbal especially there is something to be said when it comes to changing your approach. Learning all these "rules" while helpful can only take you so far, and... in a way may sometimes harm you by making you overthink.